1. Field of the Invention
The present invention relates to a color distribution measuring optical system, a color distribution measuring apparatus, and a color distribution measuring method which are applicable to evaluate the color distribution of displays, projectors, backlights, etc.
2. Description of the Related Art
In order to evaluate the color of a measurement objective (object to be measured) having a certain areal size such as a display, a projector, a backlight or the like, a system, in which color data of respective points of the measurement objective is obtained collectively, is more appropriate than a system in which the color data of respective points of the measurement objective is obtained successively or sequentially (see, for example, Japanese Patent Application Laid-open No. 2006-177812). When the visual effect, which is to be exerted on the human, is evaluated, it is possible to apply not only the spectral system in which the luminance is measured at respective wavelengths but also the tristimulus value direct reading system in which the tristimulus values are directly measured (see, for example, Japanese Patent Application Laid-open No. 2002-310800).
Therefore, it is preferable for the color evaluation to use a color distribution measuring apparatus of the tristimulus value direct reading system in which the measurement objective is photographed or imaged via an imaging optical system and a color matching function filter. In particular, the imaging optical system forms an image of the measurement objective on an image pickup element or device. The color matching function filter is a filter (x-filter, y-filter, z-filter) which is manufactured so that the shape of the curve of the spectral transmission characteristic is same as the shape of the curve of the color matching function of a normalized color system (CIE color system).
Usually, a plurality of colored glasses, which are stuck and laminated with each other, are used for the color matching function filter. However, it is difficult to control the thickness of the colored glass, and hence the manufacturing error is large. Therefore, the manufacturing cost tends to be expensive. Further, it is difficult to allow the x-filter, the y-filter, and the z-filter to have the same thickness. Therefore, a problem tends to be caused such that the measurement accuracy differs depending on the components of the tristimulus values.
In view of the above, in recent years, an investigation is started to use an optical multilayer film filter, instead of the colored glasses or stained glasses. The optical multilayer film filter is obtained by staking a plurality of dielectric multilayer films having different properties. On condition that the film arrangement or the film construction thereof is appropriately designed, the manufacturing error is small. Therefore, it is possible to suppress the manufacturing cost. Further, it is possible to allow the x-filter, the y-filter, and the z-filter to have a substantially same thickness. Therefore, the problem is not caused, which would be otherwise caused such that the measurement accuracy differs depending on the components of the tristimulus values.